The modern communications era has brought about a tremendous expansion of wireline and wireless networks. Computer networks, television networks, and telephony networks are experiencing an unprecedented technological expansion, fueled by consumer demand. Wireless and mobile networking technologies have addressed related consumer demands, while providing more flexibility and immediacy of information transfer.
Current and future networking technologies continue to facilitate ease of information transfer and convenience to users. In order to provide easier or faster information transfer and convenience, telecommunication industry service providers are developing improvements to existing networks. For example, the evolved universal mobile telecommunications system (UMTS) terrestrial radio access network (E-UTRAN) is currently being developed. The E-UTRAN, which is also known as Long Term Evolution (LTE), is aimed at upgrading prior technologies by improving efficiency, lowering costs, improving services, making use of new spectrum opportunities, and providing better integration with other open standards.
However, coverage by these new networking technologies, which may comprise packet switched networks (e.g., an Internet Protocol (IP) Multimedia Subsystem (IMS) capable network), may not be universal as they are deployed. Thus, in order to assure quality of service and avoid dropping of calls, the new networking technologies may have to coexist with legacy networking technologies, such as circuit switched (CS) networks. In this regard, a mobile terminal may have to be handed over between, for example, an LTE network and a CS network. Single radio voice call continuity (SR-VCC) procedures are being defined to enable a mobile terminal to perform an inter-domain handover from LTE to CS such that a voice over internet protocol (VoIP) session over IMS over the LTE access may be transferred to the CS network, when the LTE coverage is lost.
Heretofore, however, procedures have only been defined that may facilitate SR-VCC in an inter-domain handover for active calls. No procedures have been defined for facilitating SR-VCC in inter-domain handovers between a PS network and a CS network when a voice call is in an alerting state. In this regard, a voice call in an alerting state is an unanswered phone call, such as a ringing phone call. Accordingly, under current procedures, when SR-VCC in an inter-domain handover occurs in an alerting state call, the call may be dropped. This may pose a major inconvenience to users, as the alerting state may typically last upwards of several tens of seconds before the call is answered. For example, assume a typical call in the alerting phase lasts approximately 20 seconds and an ensuing conversation (e.g., the active phase) between parties of a voice call lasts 70 seconds. Further, setup and release phases for the voice call may last approximately 10 seconds. Therefore, since an average voice call including setup, alerting, conversation, and release phases may last 100 seconds and 20 seconds of that is the alerting state, 20 percent of all SR-VCC occurrences may occur in the alerting phase.
Systems, methods, apparatuses, and computer program products for facilitating voice call continuity in intersystem handover are therefore provided herein that may address at least some of the deficiencies described above.